Recent biomedical research has focused on proteomics, with an emphasis on the diagnosis and treatment of diseases by determining the expression profiles of disease-related proteins. Methods and technologies of identifying and quantifying proteins and comparing expression levels of proteins have thus become important. Various technologies have been developed to accommodate such proteomic research, many of which include the use of mass spectrometry.
For example, U.S. Pat. No. 6,379,970 relates to a method of detecting peptide fragments of proteins that are differentially present in biological samples. The patent states that the identity of the peptides may be determined and correlated with the proteins that are differentially present in the samples.
U.S. Patent Application Publication No. U.S. 2002/0076817 relates to methods useful in the labeling of multiple polypeptide samples and subsequent analysis of the samples by mass spectrometry, particularly in the high throughput proteomic setting.
U.S. Patent Application Publication No. 2002/0192720 relates to methods using gel electrophoresis and mass spectrometry for the rapid, quantitative analysis of proteins or protein function in mixtures of proteins derived from two or more samples in one unit operation.
U.S. Patent Application Publication No. 2003/0044864 relates to proteomics and mass spectrometry technology. The publication states that the invention provides methods for determining polypeptide profiles and protein expression variations and methods of simultaneously identifying and quantifying individual proteins in complex protein mixtures by selective differential labeling of amino acid residues followed by chromatographic and mass spectrographic analysis.
Although many new technologies have been developed, it would be advantageous to provide improved methods for quantitative analysis of peptides and proteins that do not require separation techniques such as chromatography or electrophoresis.